Embodiments of the present invention relate generally to a power flow in a power system. More specifically, the embodiments relate to damping of power system oscillations.
The power system is a complex network comprising of numerous generators, transmission lines, a variety of loads and transformers. With increasing power demand in the power system, some transmission lines are more stressed than was planned when they were built. Since stressed conditions can lead a system to unstable conditions, power system stability has become an important issue. In simple terms, power system stability is defined as the ability of the power system to return to a normal state after a disturbance. The disturbance may be a fault, a loss of a generator or even a sudden increase in power loading.
Small signal stability is a power system stability issue related to low frequency oscillations between generator rotors. It has been the main reason for many power blackouts across the world including the Western Electricity Co-ordination Council (WECC) blackout of 1996. When the power system is heavily loaded, it often exhibits multi-mode oscillations because machine rotors, behaving as rigid bodies, oscillate with respect to one another using the electrical transmission lines between them to exchange energy. These oscillations generally lie in a frequency range between 0.1-3 Hz. The oscillations in this frequency range are generally analyzed in two main oscillation modes: 1) a local mode in the range of 1 to 3 Hz i.e., a generator or a group of generators in a plant swinging against the rest of the system and 2) an inter area mode in the range of 0.1 to 1 Hz i.e., machines in one group oscillate against machines in another group.
In some embodiments, an automatic voltage regulator (AVR) or flexible alternating current system (FACTS) devices are used to damp out the oscillations and improve the power system stability. To effectively damp out the oscillations it is desirable for controllers such as power system stabilizers (PSS) of AVR and FACTS devices to separate a measurement signal of mixed frequencies such as voltage, current or power into various oscillation modes and frequencies and further identify the phase of each separate signal.
Multiple solutions are available for determining values of different frequencies or modes. However, for separating the exact signals or for identifying the exact phase of the signal, not many solutions are available. One of such solutions is to utilize a Finite Impulse Response (FIR) filter tuned to certain frequencies to extract those frequencies from a mixture of frequencies. However, due to frequency domain approach which is limited by the decimation of unwanted frequencies with a per decade decay, it is almost impossible to extract frequencies which are very close to each other. Frequency domain filters with very high orders may be able to provide some solution, but with the increase in the order of the filter, the delay associated with the filtering increases, which results in longer waiting time before the signals can be separated.
For these and other reasons, there is a need for the present invention.